Micro 100 QTHM-820L Boring & Grooving Bar Holders; Inside Diameter (Inch): 1/2 ; Inside Diameter (Decimal Inch): 0.5000 ; Outside Diameter (Decimal Inch - 4 Decimals): 20.0000 ; Overall Length (Decimal Inch): 5.8000 ; Head Diameter (Decimal Inch): 1.